Add mirror node gas estimate and contract call query APIs to the SDK docs

[SimiHunjan]

Problem

Two APIs will be introduced to the SDKs that will help developers do the following:

1. MirrorNodeContractCallQuery - Executes a contract call.
2. MirrorNodeContractEstimateGasQuery - Estimates gas usage for a contract call.

These new APIs can be documented under the Smart Contracts section under SDKs.

There should be content updated in the core concepts section that highlighting that estimates for gas can be done.

Solution

See above

Alternatives

No response